The present invention relates to a device for checking the evaluation circuit for automatic switching operations of illumination devices in vehicles.
From German Published Patent Application No. 195 23 262 A1, a device according to the species for the automatic switching of illumination devices in vehicles is known. In this context, a sensor device is provided which contains a global sensor for detecting the light conditions in the environment of the vehicle and a directional sensor for the directed detection of the light conditions in the direction of travel in front of the vehicle. The signals of the sensor device are supplied to an evaluation circuit to determine whether a change in the switching state of the illumination devices is necessary. In this known evaluation circuit, executed using analog technology, no monitoring of correct functioning is available.
The task of the present invention is to monitor the analog evaluation circuit for the automatic light switching.
The device according to the present invention for checking the evaluation circuit for automatic switching operations of illumination devices in vehicles advantageously establishes whether the evaluation device is functioning correctly. In this manner, the following defect is eliminated: in the event the analog evaluation circuit for the automatic switching operation for the illumination device of the vehicle breaks down, i.e., the analog evaluation circuit does not detect the safety-critical condition xe2x80x9ctwilightxe2x80x9d or xe2x80x9cnight,xe2x80x9d the low beam might not be switched on, for example, by a control unit for the low beam. The present invention therefore monitors this safety-critical evaluation circuit and, in the event of its not functioning, initiates further measures.
In this way, the control unit for the low beam can be informed that the evaluation circuit is defective. To remove this defect, the illumination device can be activated by this low-beam control unit and, in addition, an information message can be directed to the driver of the vehicle regarding the problem.
According to the present invention, the voltage supply for the sensor unit is interrupted for short durations at predetermined intervals for checking the evaluation circuit, which operates in analog technology, as a result of which the condition xe2x80x9cnightxe2x80x9d is simulated, and, when the evaluation circuit is operating correctly, this is detected by the latter as such, whereas, when the evaluation circuit is not functioning correctly, a signal is generated, directing attention to the defective functioning and setting in motion further steps.
According to one embodiment of the device according to the present invention, a microcontroller is provided, which, for checking purposes, causes the short-duration interruption of the voltage supply to the sensor device at predetermined intervals via a predetermined output. The output signal of the analog evaluation circuit is supplied to the microcontroller at a predetermined input as the input signal, and the microcontroller emits a signal at an output for bringing about further steps.
In accordance with another embodiment of the device according to the present invention, the output signal of the microcontroller, generated when the evaluation circuit is not functioning correctly, is supplied to a control unit for the low beam, the evaluation circuit initiating the further steps. Further steps of this type can be, for example, the automatic switching on of the low beam as well as the supplying of information to the driver of the vehicle regarding the abnormal functioning of the analog evaluation circuit.
In accordance with yet another embodiment of the device according to the present invention, the microcontroller reads in the output signal of the evaluation device via an analog/digital input, a predetermined number of increments corresponding to a predetermined voltage, for example, 255 increments corresponding to 5 V, and when the output signal of the evaluation device lies above a predetermined limit value, the device is functioning correctly, i.e., in response to the intentionally carried out voltage interruption, the simulated condition xe2x80x9cnightxe2x80x9d is detected, and, if this is not the case, the signal for initiating further steps is generated by the microcontroller.
In addition, according to another embodiment of the present invention, a second checking can be undertaken which particularly detects defects arising due to shunting with respect to the supply voltage or the ground. For this purpose, the analog/digital values detected by the microcontroller, supplied by the evaluation circuit, are checked as to whether they lie above a lower threshold value. This checking is carried out in a very advantageous manner, the lower limit value being one that is determined by the hardware.
In a further embodiment of this additional checking operation, for example, in response to a shunt with respect to the supply voltage or ground, when the checked lower limit value is not exceeded by the microcontroller, a signal is generated, which indicates the faulty functioning of the evaluation circuit and which, if appropriate, is used by the low-beam control unit for bringing about further steps.
According to a further embodiment of the present invention, a third checking operation can be carried out, which aids in checking the analog/digital converter unit, which converts the analog values delivered by the evaluation circuit into digital values. For this purpose, it is provided that the analog/digital converter unit, which converts analog values supplied by the evaluation circuit into digital values, is checked with respect to its performance reliability, and that, when it is not functioning correctly, the microcontroller at its output generates a signal for bringing about further steps.
According to an implementation of this third checking operation, it is provided that when the analog/digital converter unit of the microcontroller is used, the converter unit is checked by the cyclical supply of a voltage familiar to the microcontroller, the voltage being selected preferably in the middle range between the upper and lower reference voltage. Preferably, for taking account of the tolerances of the individual components for the checking operation in the middle range, an upper and a lower threshold value are established.